1. Field of the Invention
This invention relates to a video player of the type that produces a video output signal representative of a sequence of still pictures recorded on a magnetic disk.
2. Description Relative to the Prior Art
A still video recording format has been proposed in which a small, flexible magnetic disk is used to store up to 50 still video pictures. The still video pictures originate with an electronic camera or by transfer from another media (e.g., photographic film). The recording format provides the option of storing a full frame (two circular tracks per picture) for 25 pictures, or a single field (one circular track per picture) for 50 pictures. Which option is selected for a given disk (or a given track on the disk) is indicated by a data signal that is recorded with each video picture.
The pictures are played back by inserting the recorded disk into a video disk player, which converts the video signals recorded on the disk into a suitable format (e.g., NTSC) television signal. If the player is assured of receiving only single field recordings, it can take the form of the single head machine disclosed in U.S. Pat. No. 4,470,076. Though only one field is recorded, it still is desirable to generate a full frame (two field) output signal for conventional display circuits. In this patent, the second (interlace) field is interpolated from successive lines of the first (recorded) field. Since, however, the proposed recording format accommodates a full frame as well as a single field, it is desirable to provide two playback heads intimately spaced for sensing the field signals on two adjacent circular tracks. With a proposed track pitch of 0.1mm, mounting two heads so closely complicates mechanical assembly and encourages electrical problems such as crosstalk. To avoid such problems, U.S. Pat. No. 4,481,543 proposes dithering--on a field-by-field basis--a single head between adjacent tracks in order to provide a sequence of alternating field signals. This solution, however, introduces its own mechanical problems, since the head must be shifted between tracks during the vertical blanking period with time to settle before beginning playback of the recorded video signal.
Adding to these problems, the contemplated use of either a single or dual head can lead to significant track wear. Continued passage of the head over the same track applies enough stress and wear to the magnetic coating to eventually change its magnetic properties and thereby reduce signal output (at worst, the head can scrape the magnetic coating from the track).
An intermediate storage device, such as a field or frame store, can be used as a source for display in lieu of the signals recorded on a magnetic disk and, resultantly, in lieu of continued passage of the head(s) over the same tracks(s). In U.S. Pat. No. 4,451,857, a series of field stores are used to accumulate a four-field rendition of a still picture from a magnetic disk at non-video rates. With the field stores acting as time base buffers, readout is provided from them at video rates. In addition, field or frame stores open up a variety of other processing capabilities (see U.S. Pat. Nos. 4,302,776; 4,163,249; 4,148,070; and British Pat. No. 2,029,665).